Blast Plug

ABSTRACT

This invention relates to a blast plug (10). The blast plug (10) includes a body (12), a means for suspending the blast plug (10) in a blast hole (50) above an explosive charge (54) and a bag member (16). The body (12) comprises a first end (18), an opposing second end (20) and one or more sides tapering (22) from the first end (18) towards the second end (20). The blast plug (10) suspending means is located at least partially at the second end (20) of the body (12). The bag member (16) is attached to the tapering sides (22) of the body (12) and extends about the body (12) such that the attached portion of the bag member (16) is restricted from moving toward the first end (18) of the body (12) by the tapering sides (22) thereof, wherein the bag member (16) operatively catches and contains tamping material deposited down the blast hole (50). In use, with the blast plug (10) suspended in the blast hole (50) by the blast plug (10) suspending means, the tamping material caught and contained in the bag member (16) causes the bag member (16) to expand radially outwardly relative to the body (12) to abut and seal against the blast hole walls (56) thereby to confine the blast energy generated on detonation of the explosive charge (54), with the first end (18) of the body (12) acting to reflect pressure waves propagating from the detonated explosive charge (54) back down the blast hole (50) thereby to increase the efficiency of the explosion.

BACKGROUND OF THE INVENTION

This invention relates to a blast plug. More particularly, the present invention relates to a blast plug including a bag member, for receiving and retaining tamping material that is deposited into a blast hole containing such a blast plug, and a tapered body to act as a wedge for compacting such tamping material when an upward force is applied to the blast plug. Further, the invention discloses a method for utilizing such a blast plug.

Blast plugs having a body with a bag member connected thereto are known in the art. One example of such a device is taught by D.D. Porter in U.S. Pat. No. 4,464,993, with the bag member being in the form of a bag for containing concrete slurry. The purpose of the bag is to retain the concrete slurry until such material has dried and hardened to form an effective seal of the blast hole.

Installation of the aforementioned device is time consuming, and requires skilled operators to utilize effectively. The method of installing such a device includes mounting the device inside a covering tube, filling the bag with concrete slurry and suspending such assembly in a blast hole with a device capable of supporting such a load. Once the assembly reaches the desired level, the tube is pulled out of the blast hole to release the device at the lowered position, allowing the bag to expand in diameter into abutment with the blast hole walls in a sealing manner. Thereafter, the concrete slurry is allowed to dry before an explosive charge disposed within the blast hole is detonated.

Blast plugs having a body that is tapered to act as a wedging element when exposed to pressure are also known. These devices typically include additional members formed of hard material to cooperate with the tapered body, such that the body may be forced in between the additional members for the members to jointly expand in cross-sectional diameter as the body is driven deeper between the additional members. An example of such a device is disclosed by M. Gotham in U.S. Pat. No. 137,196. The inclusion of additional members to cooperate with the body limits the flexibility of such devices as all the members are preformed and accordingly only limited adjustments can be made to suit the specific requirements of a blast hole. These devices are costly to manufacture due to the multiple parts and are difficult to transport as they are generally formed of heavy, solid materials.

Installation of such a device includes firstly the step of lowering the wedging member, flanked by the two additional members, into a blast hole. Thereafter, an explosive charge is detonated below the device, forcing the wedging member upward wedging the two additional members outwardly and into abutment with the walls of the blast hole to lock the device in place.

Accordingly, it is an object of this invention to address the aforementioned drawbacks of the known prior art devices, and to provide a device that is effective and inexpensive, as well as simple and fast to install without the need for additional machinery.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the invention there is provided a blast plug including:

-   -   a body having a first end, an opposing second end and one or         more sides tapering from the first end towards the second end;     -   a means for suspending the blast plug in a blast hole         operatively above an explosive charge, the blast plug suspending         means being located at least partially at the second end of the         body; and     -   a bag member attached to the tapering sides and extending about         the body such that the attached portion of the bag member is         restricted from moving toward the first end of the body by the         tapering sides thereof, wherein the bag member operatively         catches and contains tamping material deposited down the blast         hole;         such that in use, with the blast plug suspended in the blast         hole by the blast plug suspending means, the tamping material         caught and contained in the bag member causes the bag member to         expand radially outwardly relative to the body to abut and seal         against the blast hole walls thereby to confine the blast energy         generated on detonation of the explosive charge, with the first         end of the body acting to reflect pressure waves propagating         from the detonated explosive charge back down the blast hole         thereby to increase the efficiency of the explosion.

The body may be frustum or frustoconical in shape.

Preferably, the first end of the body is substantially flat for, in use, effectively reflecting pressure waves propagating from the detonated explosive charge back down the blast hole.

In one embodiment, the blast plug suspending means may comprise: (i) a bore defined by the body and extending through the first and the second ends of the body; and (ii) a line disposed within the bore, the line having a locating formation for locating the body at a predetermined location along the line. Generally, the locating formation along the line is variable such that the location of the body along such line is consequentially variable.

In another embodiment, the blast plug suspending means may comprise a line cast into the body, the line extending from the body at a location at or near the second end thereof. Typically, an end of the line cast into the body is attached to a locating formation, which locating formation acts to anchor the line in the body. Preferably, the locating formation is a knot in the line, a loop in the line, a rod, a washer or any locating member extending radially outwardly on the line on which the body is cast, fastened or supported.

In yet another embodiment of the invention, the blast plug suspending means may comprise a line and a connector to which the line is connectable, the connector being cast into the body. Generally, the connector defines a loop or hook formation to which the line is connectable. More specifically, the connector may be a normal bolt, an eyebolt or a bolt with a hook formation thereon.

The bag member is preferably attached to the tapering sides of the body at a location nearer the first end than to the second end of the body.

Preferably, the bag member is a bag having an open end and a closed end, the body being disposed at least partially within the bag with the second end of the body directed toward the open end of the bag, and further wherein the bag is tied to the tapering sides of the body.

In an alternative embodiment, particularly where solid explosives are used, the blast plug may include a means for suspending a charge at a predetermined distance below the body. Generally, the charge suspending means comprises a charge line from which the explosive charge is suspended from the body.

The charge line may be an independent line extending outwardly from the first end of the body, or alternatively integral with the line from which the blast plug is operatively suspended, such that such line comprises:

-   -   (i) a first portion extending from the second end of the body;         and     -   (ii) a second portion extending from the first end of the body.

Preferably, the blast plug suspending means includes a cross member from which an end of the line opposite the end extending from the body is fastenable thereby to operatively suspend the blast plug from the cross member, which cross member is: (i) sized larger than a diameter of the blast hole; and/or (ii) configured relative to the blast hole to lie across an opening thereof; such that the cross member is restricted from falling into the blast hole.

According to a second aspect of the invention, there is provided a method for tamping a blast hole including the steps of:

-   -   (A) suspending a blast plug, as described above, in a blast hole         above an explosive charge;     -   (B) depositing tamping material down the blast hole so as to be         caught and contained by the bag member thereby to cause the bag         member to expand radially outwardly to abut and seal against the         blast hole walls; and     -   (C) applying an operatively upward force to the blast plug to         displace the blast plug body further into the tamping material,         consequentially causing the tamping material riding along the         tapered sides of the body to displace radially outwardly         relative to such body in a wedge-like manner thereby to further         force the bag member into sealing abutment with the blast hole         walls.

It will be appreciated that the operatively upward force may be one or both of: (i) an upward pulling force applied to the blast plug via the blast plug suspending means prior to detonation of the explosives; and (ii) an upward pushing force generated by the detonation of the explosive.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a blast plug in accordance with the present invention;

FIG. 2 is a cross-sectional side view of the blast plug of FIG. 1;

FIG. 3 is a cross-sectional side view of an alternative embodiment of a blast plug in accordance with the present invention;

FIG. 4 is a cross-sectional side view of yet another embodiment of a blast plug in accordance with the present invention;

FIG. 5 is a cross-sectional side view of the blast plug of FIG. 1 being deployed in a blast hole (not to scale);

FIG. 6 is a cross-sectional side view of the blast plug of FIG. 1 deployed in the blast hole (not to scale) and being loaded with tamping material;

FIG. 7 is a cross-sectional side view of the blast plug of FIG. 1 deployed in the blast hole and displaced upwardly into the tamping material, to cause the blast plug to wedge against the blast hole walls; and

FIG. 8 is a perspective view of a further alternative embodiment of a blast plug in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A blast plug according to a preferred embodiment of the invention is designated generally in FIG. 1 by reference numeral 10. The blast plug 10 comprises a body 12, a means for suspending the blast plug, which suspending means includes a line 14, and a bag member 16.

The body 12 includes a first end 18, an opposing second end 20 and tapering sides 22 extending between the ends 18, 20 such that the body 12 is frustum in shape, more preferably frustoconical in shape.

The bag member 16 is attached to the tapering sides 22 by a tie 24, which inhibits the movement of the bag member 16 along the tapering sides 22, particularly to restrict the bag member 16 from sliding along the tapering sides 22 and beyond the first end 18 when loaded with tamping material 52 as will be described hereinafter. It is particularly preferred that the bag member 16 be attached to the tapering sides 22 at a location nearer the first end 18 than to the second end 20 of the body 12.

The bag member 16 is made of a flexible material to enable the bag member 16 to deform into the shape of the surface of the blast hole walls 56. The bag member 16 extends about the body 12 and is sized and shaped to extend from the body 12 to blast hole walls 56 and partially along such blast hole walls 56. This enables the bag member 16 to act as a catch for catching and containing tamping material 52 that is deposited into the blast hole 50 in which the blast plug 10 is deployed, as will be described with reference to FIG. 6. This configuration further enables the second end 20 of the body 12 and the line 14 to be enclosed within the bag member 16 when the blast plug 10 is not in use.

The line 14 is used for suspending the blast plug 10 in a blast hole 50 as will be described with reference to FIGS. 5 to 7. The line 14 may be connected to the body 12 in a multitude of ways, but is always located at least partially at the second end 20, such that the body 12 is always suspended with the first end 18 directed towards the explosive charge 54. It is further preferred that the first end 18 of the body 12 is substantially flat and sized to fit the blast hole 50 snugly. In this manner, the pressure waves propagating from detonated explosive charge 54 are reflected back down the blast hole 50 and the efficiency of such explosion is increased.

According to a first embodiment illustrated in FIG. 2, the line 14 may be connected to the body 12 by placing the line 14 within the body 12 during casting of the body 12. FIG. 2 additionally shows a locating formation 26 in the form of a rod extending transversely through the line 14, which rod 26 acts to anchor the line 14 in the body 12. It will be appreciated that the locating formation 26, instead of being a rod, may be of an alternative form, for example a knot in the line 14.

Referring now to FIG. 3, an alternative method of connection of the line 14 to the body 12 is shown. Herein, the body 12 defines a bore 28 which may be formed in the body 12 during casting or drilled therethrough after forming of the body 12. The line 14 is disposed within the bore 28 and extends through the body 12 beyond both the first and second ends 18, 20, with a locating formation 26, in the form of a knot, located in abutment with the first end 18 of the body 12. It will be appreciated that the locating formation 26, instead of being a knot, may be of an alternative form, for example a rod, a washer or such other suitable member.

Additionally, in the embodiment of FIG. 3, the bag member 16 is a bag wherein the body 12 is disposed with the second end 20 directed towards an open end of the bag 16 and the line 14 extending through an aperture (not shown) defined in an opposing closed end of the bag 16. It will be appreciated that the location of the locating formation 26 along the line 14 is variable, such that the location of the body 12 along the line 14 is consequentially variable.

In FIG. 4 an alternative embodiment is illustrated, wherein the suspending means is a connector having a hook 30 to which the line 14 is connectable. The hook 30 is connected to the body 12 at the second end 20 by placing the hook 30 within the body 12 during casting or through mechanical means after forming of the body 12. The bag member 16 is again illustrated as a bag, with the body 12 disposed therein.

The method of tamping a blast hole 50 with the blast plug 10 in accordance with the present invention will now be explained with reference to FIGS. 5 to 7.

With reference to FIG. 5, the blast plug 10 is suspended in a blast hole 50 by line 14 extending from the second end 20 of the body 12 and a cross member 31 located at an opening of the blast hole 50. It will be appreciated that the blast plug 10 is operatively suspended in the blast hole 50 such that the first end 18 thereof is spaced from the explosive charge 54 by a suitable off distance, to define between the explosive charge 54 and the blast plug 10 a standoff void 55 that is at least partly filled with air (or other gas) or a liquid, such as water. The bag member 16 is displaced along the blast hole 50 as the body 12 is lowered toward the intended location. The bag member 16 flares outwardly from the body 12 to extend from the tapering sides 22 to the blast hole walls 56.

Once the blast plug 10 has reached the intended location within the blast hole 50, tamping material 52 is deposited into the blast hole 50. As the tamping material 52 falls down the blast hole 50 it is caught by the bag member 16 and retained therein to inhibit the tamping material 52 from falling past the body 12 toward the explosive charge 54. As the bag member 16 receives tamping material 52, it fills and expands radially outwardly toward the blast hole walls 56, causing the bag member 16 and the tamping material 52 contained therein to abut and seal against the blast hole walls 56. In this manner, an effective seal is created across the entire inner cross-sectional surface of the blast hole 50 as illustrated in FIG. 6.

With sufficient tamping material 52 contained within the bag member 16, a pulling force may be applied to the line 14, causing the body 12 to be displaced toward and into the tamping material 52 into the position illustrated in FIG. 7. As the body 12 is displaced into the tamping material 52, it acts as a wedging member with the tamping material 52, riding along the tapered sides 22, being forced radially outwardly, consequentially compressing the tamping material 52 between the body 12 and the blast hole walls 56, further forcing the bag 16 into sealing abutment against the blast hole walls 56.

With the blast plug 10 deployed as described with reference to FIG. 7, the explosive charge 54 is detonated and expels energy in the form of pressure waves toward the blast plug 10. As the pressure waves propagate through the blast hole 50 and into contact with the substantially flat first end 18 of the body 12, the waves are reflected back down the blast hole 50 to increase the efficiency of the explosion and reduce expulsion of material from the blast hole 50. Further, as the pressure waves exert an upward force on the body 12, the body 12 is displaced deeper into the tamping material 52, further compressing the tamping material 52 through the wedge-like action of the tapered sides 22 and further increasing the efficiency of the seal between the bag member 16 and the blast hole walls 56.

It will be appreciated that the explosive charge 54 is typically pumped into the blast hole 50 in a liquid form, and detonated in use by a detonator 58. It will be appreciated further that a detonator cord 60 of the detonator 58 may be suspended from the cross member 31 much the same as the manner in which the blast plug 10 is suspended therefrom.

With reference to FIG. 8, with like references designating like parts, the blast plug 110 further includes a means 132 for suspending the explosive charge 154, which charge suspending means comprises a line 132 extending from the first end 118 of the body 112 for suspending the explosive charge 154 therefrom. With this configuration, the standoff distance by which the body 112 and the explosive charge 154 is spaced from one another can be controlled by adjusting the length of the line 132 as may be required for optimal efficiency of a blast.

It is envisaged that the main application of the blast plug 10 will be in the field of mining, particularly for coal and hematite fragmentation. The advantages of the blast plug 10 are many. A list of some of the advantages are listed below:

-   -   Economical and eco-friendly manufacture—the body 12 can be         moulded from concrete, reinforced concrete or mixed with         vermiculite if required, using moulds that create a         frustoconical shape such as bottles, flower pots or other         cone-like shaped moulds. It will be appreciated that the blast         plugs, particularly the first ends 28 thereof, are sized to fit         snugly into the desired size blast hole. The bag members 16 may         be polypropylene bags, plastic bags, conveyor belts or tyres. It         will be appreciated further that the bottles, flower pots, bags,         conveyor belts and tyres used to manufacture the blast plugs may         be sourced from previously discarded material, which may be         recycled for this purpose.     -   Flexibility of manufacture—the line 14, or at least a portion         thereof, may be made from wire, chain or rope.     -   Environmentally friendly and safe in use—reduced emission from         the blast holes of gasses that are responsible for earth warming         (i.e. carbon monoxide, carbon dioxide and nitrogen oxide).     -   Optimal rock fragmentation size. A minimum amount of explosives         charge is required with an increased air or water standoff         distance between the blast plug and the explosives charge to         achieve the desired blasted ore size.     -   Reduced unwanted fines, which negatively impacts on the price of         the ore (particularly in hematite, manganese and coal mining).     -   Reduction in contamination between the tamping material and the         explosives.     -   The weight of the tamping material is carried by the blast plug         and as such, no longer supported by the explosives, which         ensures a lighter explosives density at the bottom of the blast         hole and an improved initiation by a booster charge that will         result in improved Velocity of Detonation and improved         fragmentation.     -   Improved mining floor conditions.     -   Improved cast blast or throw of the blasted rock.     -   Reduced air blast noise.     -   Reduced vibrations as measured by seismographs (confirmed         through testing).     -   Reduced fly rock.     -   Reduced side and back break.     -   Improved and safer high wall mining conditions.     -   Improved machine digging rates.     -   Reduced wear & tear on mining machines and mineral sizes.     -   Increased productivity and increased production rates.     -   Improved mining profits.     -   The cross members are eco-friendly and will not damage mining         machine tyres or cut conveyor belts—the cross member are         typically made from wooden sticks.     -   Mixed and casted with vermiculite, heat resistant plugs will be         manufactured to seal off hot holes encountered in blasting.

Although the invention has been described with reference to a preferred embodiment, it will be appreciated that many modifications or variations of the invention are possible without departing from the spirit or scope of the invention. 

1. A blast plug including: a body having a first end, an opposing second end and one or more sides tapering from the first end towards the second end; a means for suspending the blast plug in a blast hole operatively above an explosive charge, the blast plug suspending means being located at least partially at the second end of the body; and a bag member attached to the tapering sides and extending about the body such that the attached portion of the bag member is restricted from moving toward the first end of the body by the tapering sides thereof, wherein the bag member operatively catches and contains tamping material deposited down the blast hole; such that in use, with the blast plug suspended in the blast hole by the blast plug suspending means, the tamping material caught and contained in the bag member causes the bag member to expand radially outwardly relative to the body to abut and seal against the blast hole walls thereby to confine the blast energy generated on detonation of the explosive charge, with the first end of the body acting to reflect pressure waves propagating from the detonated explosive charge back down the blast hole thereby to increase the efficiency of the explosion.
 2. A blast plug according to claim 1, wherein the body is frustum shaped.
 3. A blast plug according to claim 1, wherein the body is frustoconical in shape.
 4. A blast plug according to claim 1, wherein the first end of the body is substantially flat for, in use, effectively reflecting pressure waves propagating from the detonated explosive charge back down the blast hole.
 5. A blast plug according to claim 1, wherein the blast plug suspending means comprises: (i) a bore defined by the body and extending through the first and the second ends of the body; and (ii) a line disposed within the bore, the line having a locating formation for locating the body at a predetermined location along the line.
 6. A blast plug according to claim 5, wherein the position of the locating formation along the line is variable such that the location of the body along such line is consequentially variable.
 7. A blast plug according to claim 1, wherein the blast plug suspending means comprises a line cast into the body, the line extending from the body at a location at or near the second end thereof.
 8. A blast plug according to claim 7, wherein an end of the line cast into the body is attached to a locating formation, which locating formation acts to anchor the line in the body.
 9. A blast plug according to claim 8, wherein the locating formation is a knot in the line, a loop in the line, a rod, a washer or any locating member extending radially outwardly on the line on which the body is cast, fastened or supported.
 10. A blast plug according to claim 1, wherein the blast plug suspending means comprises a line and a connector to which the line is connectable, the connector being cast into the body.
 11. A blast plug according to claim 10, wherein the connector defines a loop or hook formation to which the line is connectable.
 12. A blast plug according to claim 1, wherein the bag member is attached to the tapering sides of the body at a location nearer the first end than to the second end of the body.
 13. A blast plug according to claim 1, wherein the bag member is a bag having an open end and a closed end, the body being disposed at least partially within the bag with the second end of the body directed toward the open end of the bag, and further wherein the bag is tied to the tapering sides of the body.
 14. A blast plug according to claim 10, further including a means for suspending a charge at a predetermined distance below the body.
 15. A blast plug according to claim 14, wherein the charge suspending means comprises a charge line from which the explosive charge is suspended from the body.
 16. A blast plug according to claim 15, wherein the charge line is an independent line extending outwardly from the first end of the body, or integral with the line from which the blast plug is operatively suspended, such that such line comprises: (i) a first portion extending from the second end of the body; and (ii) a second portion extending from the first end of the body.
 17. A blast plug according to claim 10, wherein the blast plug suspending means includes a cross member from which an end of the line opposite the end extending from the body is fastenable thereby to operatively suspend the blast plug from the cross member, which cross member is: (i) sized larger than a diameter of the blast hole; and/or (ii) configured relative to the blast hole to lie across an opening thereof; such that the cross member is restricted from falling into the blast hole
 18. A method for tamping a blast hole including the steps of: (A) suspending a blast plug in accordance with claim 1 in a blast hole above an explosive charge; (B) depositing tamping material down the blast hole so as to be caught and contained by the bag member thereby to cause the bag member to expand radially outwardly to abut and seal against the blast hole walls; and (C) applying an operatively upward force to the blast plug to displace the blast plug body further into the tamping material, consequentially causing the tamping material riding along the tapered sides of the body to displace radially outwardly relative to such body in a wedge-like manner thereby to further force the bag member into sealing abutment with the blast hole walls.
 19. A method according to claim 17, wherein the operatively upward force is one or both of: (i) an upward pulling force applied to the blast plug via the blast plug suspending means prior to detonation of the explosives; and (ii) an upward pushing force generated by the detonation of the explosive.
 20. A blast plug according to claim 6, wherein the locating formation is a knot in the line, a loop in the line, a rod, a washer or any locating member extending radially outwardly on the line on which the body is cast, fastened or supported.
 21. A blast plug according to claim 5, further including a means for suspending a charge at a predetermined distance below the body.
 22. A blast plug according to claim 7, further including a means for suspending a charge at a predetermined distance below the body.
 23. A blast plug according to claim 5, wherein the blast plug suspending means includes a cross member from which an end of the line opposite the end extending from the body is fastenable thereby to operatively suspend the blast plug from the cross member, which cross member is: (i) sized larger than a diameter of the blast hole; and/or (ii) configured relative to the blast hole to lie across an opening thereof; such that the cross member is restricted from falling into the blast hole
 24. A blast plug according to claim 7, wherein the blast plug suspending means includes a cross member from which an end of the line opposite the end extending from the body is fastenable thereby to operatively suspend the blast plug from the cross member, which cross member is: (i) sized larger than a diameter of the blast hole; and/or (ii) configured relative to the blast hole to lie across an opening thereof; such that the cross member is restricted from falling into the blast hole 